Can a fat transfer be done to the hips and breasts at the same time?

Fat transfers to more than one site are typically safe and not uncommon. Limiting factors are the volume of fat you have available for donors and the added discomfort from multiple area treatment.

The longer answer is that 1) you need to have an adequate amount of fat to fill both areas, and 2) that recovery is a bit more difficult since you will be restricted from placing too much pressure on the areas that were grafted, so sleeping and sitting will be a bit more cumbersome.